a Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Animal Medicine , China Agricultural University , Beijing , China.
Chronobiol Int. 2019 Apr;36(4):548-563. doi: 10.1080/07420528.2019.1566740. Epub 2019 Jan 21.
The avian circadian rhythm pacemaker is composed of the retina, pineal gland and suprachiasmatic nucleus. As an intact input-pacemaker-output system, each of these structures is linked within a neuroendocrine loop to influence downstream processes and peripheral oscillations. While our previous study found that monochromatic light affected the circadian rhythms of clock genes in the chick retina, the effect of the pineal gland on the response of the retinal circadian clock under monochromatic light still remains unclear. In this study, a total of 144 chicks, including sham-operated and pinealectomized groups, were exposed to white, red, green or blue light. After 2 weeks of light illumination, the circadian expression of six core clock genes (cClock, cBmal1, cCry1, cCry2, cPer2 and cPer3), melanopsin (cOpn4-1, cOpn4-2), Arylalkylamine N-acetyltransferase (cAanat) and melatonin was examined in the retina. The cBmal1, cCry1, cPer2, cPer3, cOpn4-1, cOpn4-2 and cAanat genes as well as melatonin had circadian rhythmic expression in both the sham-operated and pinealectomized groups under different monochromatic lights, while cClock and cCry2 had arrhythmic 24 h profiles in all of the light-treated groups. After pinealectomy, the rhythmicity of the clock genes, melanopsins, cAanat and melatonin in the chick retina did not change, especially the mesors, amplitudes and phases of cBmal1, cOpn4-1, cOpn4-2, cAanat and melatonin. Compared to the white light group, however, green light increased the mRNA expression of the positive-regulating clock genes cBmal1, cAanat, cOpn4-1 and cOpn4-2 as well as the melatonin content in pinealectomized chicks, whereas red light decreased their expression. These results suggest that the chick retina is a relatively independent circadian oscillator from the pineal gland, whose circadian rhythmicity (including photoreception, molecular clock and melatonin output) is not altered after pinealectomization. Moreover, green light increases ocular cAanat expression and melatonin synthesis by accelerating the expression of melanopsin and positive-regulating clock genes cBmal1 and cClock.
鸟类的生物钟节律起搏器由视网膜、松果腺和视交叉上核组成。作为一个完整的输入-起搏器-输出系统，这些结构中的每一个都通过神经内分泌环相互连接，以影响下游过程和外周振荡。虽然我们之前的研究发现单色光会影响小鸡视网膜时钟基因的昼夜节律，但松果腺对单色光下视网膜生物钟反应的影响尚不清楚。在这项研究中，总共 144 只小鸡，包括假手术和松果体切除术组，暴露在白光、红光、绿光或蓝光下。光照 2 周后，在视网膜中检测到 6 个核心时钟基因（cClock、cBmal1、cCry1、cCry2、cPer2 和 cPer3）、黑视蛋白（cOpn4-1、cOpn4-2）、芳香族烷基胺 N-乙酰转移酶（cAanat）和褪黑素的昼夜表达。在不同单色光下，假手术和松果体切除术组的 cBmal1、cCry1、cPer2、cPer3、cOpn4-1、cOpn4-2 和 cAanat 基因以及褪黑素均表现出昼夜节律性表达，而 cClock 和 cCry2 在所有光照处理组中均呈现出无节律性的 24 小时谱。松果体切除后，小鸡视网膜时钟基因、黑视蛋白、cAanat 和褪黑素的节律性没有改变，特别是 cBmal1、cOpn4-1、cOpn4-2、cAanat 和褪黑素的中值、振幅和相位。然而，与白光组相比，绿光增加了松果体切除小鸡中正向调节时钟基因 cBmal1、cAanat、cOpn4-1 和 cOpn4-2 以及褪黑素含量的 mRNA 表达，而红光则降低了其表达。这些结果表明，小鸡视网膜是一个相对独立于松果腺的生物钟振荡器，其昼夜节律性（包括光感受、分子钟和褪黑素输出）在松果体切除后不会改变。此外，绿光通过加速黑视蛋白和正向调节时钟基因 cBmal1 和 cClock 的表达来增加眼部 cAanat 的表达和褪黑素的合成。
